High speed, amplitude variable thrust control

ABSTRACT

A high speed control apparatus and method utilized in a system having a high pressure fluid supply for producing precisely controlled, amplitude and duration variable thrust are disclosed, the apparatus including a co-fired piezoelectric stack connected with a control signal input, a low-loss mechanical displacement amplifier operatively associated with the stack, and a high pressure spring-loaded axial valve assembly coupled with the amplifier. A microprocessor control system and energy storage and power amplifier system are utilized to provide a calibrated output voltage control signal which drives the piezoelectric stack in such a manner as to produce rapidly changing displacements in the stack (as frequent as 10 microseconds) which are subsequently amplified by the displacement amplifier. The valve assembly is connected with the amplifier and includes a valve core which is normally forced closed upon a valve seat by a compression spring. As the piezoelectric stack expands upon application of a step change in voltage, the valve core is lifted off the seat permitting fluid to expand through the seat and create thrust that is substantially equal in duration and directly proportional in amplitude to the control signal.

FIELD OF THE INVENTION

This invention relates to loading systems, and, more particularly,relates to thrust control apparatus and methods.

BACKGROUND OF THE INVENTION

Apparatus and methods for introducing a force into a mechanicalstructure or structural system consisting of one or more rigid bodies orflexible elements have hereto for been known and/or utilized. It wouldbe advantageous for the purposes of active control and/or damping of thestructure or structural system when subjected to random and/or unwantedexcitation forces, or for the purpose of structural identification(i.e., determination of the dynamic characteristics which make aparticular structure unique such as its mode shapes and frequencies) forsuch introduced forces to be capable of following a predeterminedvariation in time which may either be harmonic or non-harmonic innature. It is furthermore advantageous, both from the control andidentification viewpoint, for the force-time history imparted to thestructure to be capable of being varied at an extremely rapid rate whilestill maintaining "intelligence", that is, a pre-determined,analytically definable shape.

For example, it has been shown that it is possible to recover thedynamic characteristics of a structure with greater reliability, and toa higher degree of precision, if the structure can be excited with aforce-time pulse which is analytically defined by an inverse gaussiandistribution (see Carasso, A. S., and Simiu, E., "Estimation of DynamicGreen's Functions For Large Space Structures By Pulse Probing andDeconvolution"). Furthermore, the ability to load the test structurewith as short (time duration) an inverse gaussian pulse as possible willenable the capture of a higher number of mode shapes, and thereforeyield more precise knowledge of the dynamic characteristics of thestructure. Such precision and speed of response of the force generationsystem is of particular use in the control of spacecraft and orbitingstructures and for the control of flexible robotic systems, although thetechnique is equally applicable to, for example, the active control of atall building subjected to earthquake loads.

It is a required characteristic of most such control/identificationloading systems that they be capable of operating without the presenceof a reaction surface, frame, or other interacting structure. Thisrequirement is most obvious for the case of the control of spacecraftand orbiting structural systems.

Existing controlled-force generation technology includes closed loopservo-hydraulic and servo-pneumatic loading equipment now in common usefor structural testing and industrial fabrication. Such equipment workson the principle of directing a pressurized fluid (either hydraulic oilor compressed air) from a pressurized reservoir to a bi-directionalactuator which may be made to either extend, contract, or remainstationary depending upon state of an electronically controlledservovalve.

While it is possible to program these actuators to impart an"intelligent" forcing function into a test structure, the time for theseactuators to respond to an instantaneous change in the command signal isgenerally about 0.020 second or longer. If it is assumed (for the sakeof later comparison) that a continuous programmed, or "intelligent",forcing function requires 100 defining grid points, then the shortestpossible programmed impulse that could be imparted to a test structureusing such loading equipment would be 2 seconds or longer. In addition,such actuators require a reaction surface in order to be used.

Alternatively, several loading systems presently exist for spacecraftwhich require no reaction surface. These fall into a broadclassification known as Reaction Control Systems (RCS). Of particularinterest to the present discussion are those reaction control systemswhich comprise small rocket thrusters which may be used fortranslational as well as rotational control of spacecraft and orbitingstructural systems.

Classical RCS thrusters employ a pressurized supply of fuel, anelectronically controlled solenoid-type valve, a combustion chamber (ifthe thruster is of a bipropellant variety) and an expansion nozzle. Thecontrol solenoids are normally closed in such systems, and only theduration of the open time is subject to variation. Therefore, whilesolenoid controlled RCS thrusters can impart differing levels of thrustduration, there is no variation in thrust level (which is controlled bythe fixed diameter of the thruster nozzle). Such systems also sufferfrom a lack of precise impulse bit repeatability due to the opening andclosing characteristics of the valves, manifold fill times, and chemicalignition delay times.

A second type of RCS thruster employs a piezoelectric pump for the twofuel components of a bipropellant thruster (see, for example, Kattchee,N., "Piezoelectric Injection System For Vernier Impulse Thrusters," June1967). This is known as the pulse-pumped vernier engine concept andoperates on the principle of pulsing a piezoelectric stack with aspecified voltage waveform. The piezoelectric stack is connected to aseries of inlet and outlet valves which permit the pump to drawpropellant into a holding chamber during a contraction of the stack andto expel the propellant through the outlet valve during an expansion ofthe stack.

Each such cycle delivers a finite, measurable quantity of fuel to acombustion chamber and subsequently to an expansion nozzle. Thefrequency of the arrival of the electrical pulses which drive thepiezoelectric stack thus determines the total impulse delivered by thethruster during a specified length of time. While this is a usefulmethod for metering precise impulses, the fastest response time thus farachieved has been on the order of 0.01 second, and thus a 100 point"intelligent" load pulse would be at least 1 second in duration, whichis too long for accurate identification of higher frequency mode shapesthat are presently of interest for spacecraft involving precise pointingrequirements. Furthermore, the amplitude (peak force) of the thrustwhich can be achieved in this manner is severely limited by the maximumstroke of the piezoelectric stack, and thus amplitude modulation toachieve an "intelligent" force-time pulse is not practicable with thisapproach.

A variety of other piezoelectric valving systems have been heretoforesuggested for use in a variety of applications (see, for example, U.S.Pat. Nos. 4,669,660, 5,029,610, 4,431,136, 5,025,766, and 3,055,631),some including amplification of the movement of the piezoelectric device(see, for example, U.S. Pat. No. 4,593,658). These systems, however,suffer many of the same impediments hereinabove noted and/or could notsuitably perform functions applicable to the systems and problemsaddressed by the instant invention.

SUMMARY OF THE INVENTION

This invention provides an apparatus and method for precisionidentification and control of flexible structures by provision of an"intelligent" forcing function with a duration, or pulse width, of lessthan 0.01 seconds and with sufficient amplitude so as to be useful forcontrol of real life engineering structures. In particular, duration andamplitude variable thrust control is provided that incorporates a veryhigh speed, electronically controllable valve system which is capable ofcontinuously metering the flow of pressurized gas and/or pressurizedpropellants through an expansion nozzle to create thrust.

The apparatus includes a valve for retaining fluid under high pressurewhen in the closed position, means for input of a control signal havinga duration and a variable parameter, structure coupled to the controlsignal means, and a displacement amplifier for amplifying displacementof the structure caused when the control signal is applied thereto. Acoupler is utilized to apply the amplified displacement for opening thevalve (preferably with the direction of valve opening movement beingopposite the direction of displacement of the structure). The apparatusis capable of a repeatable pulse duration of as little as 0.001 secondwith a lagtime between control signal generation and onset of thrust ofas little as 0.0005 second.

The expansion of fluid through the nozzle as the valve core is raisedfrom and lowered to the closed position creates (directly or indirectly)thrust which is directly proportional to the displacement of the valvecore, and therefore directly proportional to the control signal(voltage-time history) used to drive the piezoelectric stack. The actualresponse speed, or delay time, between a step change in control voltageto the stack and the corresponding change in thrust level at the nozzleis determined by the response time of the stack (as little as 10microseconds utilizing a co-fired piezoelectric stack) and thepropagation speed of the resulting stress wave to the valve tip (a lagtime of as little as 0.0004 second using the apparatus of thisinvention). A controllable (repeatable) pulse width (i.e., the totaltime from onset of measurable thrust through valve closure) is as smallas 0.001 second using this invention.

It is therefore an object of this invention to provide a high speed,amplitude variable thrust control apparatus and method.

It is another object of this invention to provide a high speed thrustcontrol apparatus and method for which the amplitude of the force-timepulse is capable of being varied over a wide spectrum of force levels ina continuous manner.

It is yet another object of this invention to provide a high speed,amplitude variable thrust control apparatus which has the capability ofapplying an arbitrary force-time pulse to a structure without the needof a reaction surface or any support infrastructure.

It is still another object of the invention to provide highly responsivecontrol of bipropellant, monopropellant, and or cold gas reactioncontrol thrusters which may be used for precision control of spacecraftand orbiting structures.

It is still another object of this invention to provide a high speed,amplitude variable thrust control apparatus including a valve forretaining fluid under high pressure when in the closed position, meansfor input of a control signal having a duration and a variableparameter, structure coupled to the control signal means, a displacementamplifier for amplifying displacement of the structure caused when thecontrol signal is applied thereto and a coupler to apply the amplifieddisplacement for opening the valve (preferably with the direction ofvalve opening movement being opposite the direction of displacement ofthe structure). It is yet another object of this invention to provide ahigh speed, amplitude variable thrust control apparatus and methodcapable of providing either continuously variable or pusled thrust witha repeatable pulse duration of as little as 0.001 second and with alagtime between control signal generation and onset of thrust of aslittle as 0.0005 second.

With these and other objects in view, which will become apparent to oneskilled in the art as the description proceeds, this invention residesin the novel construction, combination, arrangement of parts and methodsubstantially as hereinafter described, and more particularly defined bythe appended claims, it being understood that changes in the preciseembodiment of the herein disclosed invention are meant to be included ascome within the scope of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate a complete embodiment of theinvention according to the best mode so far devised for the practicalapplication of the principles thereof, and in which:

FIG. 1 is a front view of a first embodiment of the apparatus of thisinvention utilized as a cold gas thruster, portions being cutaway toshow internal elements;

FIG. 2 is a side view of the apparatus of FIG. 1 showing mounting of anonboard, embedded microprocessor control system and energy storage andcontrol system;

FIG. 3 is a top view of the apparatus of FIG. 1;

FIG. 4 is a schematic illustration of the moving internal parts of theapparatus of FIG. 1;

FIG. 5 is a detailed illustration of the high pressure valve seat of theapparatus of FIG. 1;

FIG. 6 is a detailed illustration of the high pressure valve core rodtip and valve seat of the apparatus of this invention;

FIGS. 7A, 7B and 7C are detailed illustrations of the mechanicaldisplacement amplifier used to multiply and invert the output motionfrom the piezoelectric stack as used in the apparatus of this invention;

FIG. 8 is a front view of a second embodiment of the apparatus of thisinvention utilized as a pressure fed hypergolic bipropellant thruster,portions being cut-away to show internal working elements;

FIGS. 9A and 9B are graphic illustrations of test data measuring minimumrepeatable pulse width resolution utilizing the apparatus of thisinvention;

FIG. 10 is a graphic illustration of lag time data utilizing theapparatus of this invention; and

FIG. 11 is a graphic illustration of the continuous variability ofamplitude of thrust at various continuous drive voltages (as opposed tofinite voltage pulses) achievable using the apparatus of this invention.

DESCRIPTION OF THE INVENTION

Referring now to FIGS. 1 through 4, a first embodiment 11 of theinvention is shown for use, generally, in a system as a cold gasthruster. Housing 13 anchors the invention to the structure to becontrolled or tested, and provides internal reaction points for themoving parts of the invention. Housing 13 is preferably machined from asolid block of high strength, lightweight engineering material (such asaluminum alloy), or otherwise fabricated by such processes ascentrifugal casting, injection molding or the like to provide amonolithic unit.

Mechanical action within housing 13 is initiated by input of a directcurrent voltage signal via electrical connectors 15 and 17 topiezoelectric stack 19 axially oriented in cavity 21 of housing 13.Stack 19 is preferably a monolithic (or "co-fired") piezoelectric (orelectrostrictive) stack of a type commercially available (for example, a0.375 inch by 0.375 inch by 3 inch stack made of PZT for a maximumdisplacement capability of about 0.003 inch at a full 300 volt controlsignal). Such piezoelectric stacks are presently capable of producing0.01% strain when subjected to an electric potential of approximately300 vdc. This strain is essentially fully developed within 10microseconds of the application of a step change in voltage to the stackand therefore allows for extremely rapid displacement control, providedan appropriate voltage-time history can be applied to the stack.However, 0.01% strain is insufficient for direct operation, for example,of an effective rocket engine feed line valve. To be practicable, astrain of approximately 0.1% to 0.15% would be required for directoperation of a thruster valve, and thus amplification of thedisplacement of stack 19 as set forth hereinbelow is required for suchapplications in order to retain the benefit of such rapid displacementcontrol.

Integral bearing supports 23 and 25 are affixed permanently to both endsof piezoelectric stack 19. These are preferably machined blocks of ahigh strength engineering material such as hardcoated aluminum alloy,each having a machined, tapered, circular bearing hole, or seat, towhich are affixed bearings 27 and 29 (preferably spherical bearings).Bearings 27 and 29 are preferably made of durable, lightweight materialwith low friction characteristics (for example a ruby-saphire sphere).

Mechanical displacement amplifier 31 includes stiff, anvil-shaped lever33, unidirectional flexing segment, or hinge, 35 and support 37.Amplifier 31 is monolithically fabricated from a very high strengthengineering material having a low modulus of elasticity, and is boltedto housing 13 to thereby reside within cavity 39 such that the planewhich is parallel to the face of the amplifier as shown in FIG. 1 (i.e.,perpendicular to the axis of rotation of the anvil-lever), and whichlies substantially on the centerline through the thickness of theamplifier, also lies substantially on the centerline of through thethickness (i.e., the distance between the tanks as shown in FIG. 3) ofhousing 13.

As shown in FIG. 4, top bearing 29 of piezoelectric stack 19 mates withtapered, circular bearing seat 41 in the base of threaded nut 43fabricated from a high strength engineering material such as, forexample, hardcoated aluminum alloy. Bottom bearing 27 of piezoelectricstack 19 mates with a similar tapered, circular bearing seat 45 on thetop surface of the short side of the lever 33. Threaded nut 43 is usedto adjust the vertical position of piezoelectric stack 19 with respectto lever 33 to insure that stack 19 is in compression contact with lever33 at all operative times. PG,17 As may be appreciated, bearings 27 and29 are thus used to insure that all load is transmitted axially throughpiezoelectric stack 19 to lever 33 and to allow for rotation thereofabout hinge 35 without the consequent development of significantresistance to such motion at bearing 27.

Furthermore, bottom bearing 27 and top bearing 29 are positioned in sucha manner so as to orient the longitudinal axis of piezoelectric stack 19in an initially perpendicular orientation with respect to the plane ofthe top surface of lever 33

Spherical bearing 47 is maintained in bearing seat 49 in the end of thelong side of lever 33 and is in compressive contact with tapered,circular bearing seat 51 in top face 53 of interior slot 55 in core rodcoupler 57, through which the long end of lever 33 passes. Core rodcoupler 57 is fabricated from a high strength, lightweight engineeringmaterial, such as hardcoated aluminum alloy, and has threaded holes 59and 61 formed at its top and bottom, respectively, to which are affixedguide rod 63 and valve core rod 65, respectively.

Valve core rod 65 is normally held in contact with seat 67 by means ofcompression spring 69 which reacts against threaded plug 71 which is inturn screwed into threaded borehole 73 on the centerline through thethickness of housing 13. Threaded plug 71 is used to adjust the level ofprecompression exerted by valve core rod 65 on valve seat 67. Normallythis level of precompression is that required to insure that no leakageof high pressure gas and/or propellant occurs at valve seat 67. Guiderod 63 is received in threaded hole 59 on the top of core rod coupler 57and passes through compression spring 69 and into guide hole 75 which ismachined through the centerline of threaded plug 71.

Guide hole 77 having valve core rod 65 therein is machined from housing13 and communicates with borehole 73 and pressure chamber 79. Guideholes 75 and 77 guide and constrain the motion of valve core rod 65,guide rod 63 and core rod coupler 57. Guide rod 63 and valve core rod 65are preferably fabricated from a very high strength, high hardnessmaterial, for example Vascomax 240 or similar high strength, hardenedsteel alloys.

In the embodiment of the invention depicted in FIGS. 1 through 3, wherethe invention is to be operated as a cold gas thruster, onboard highpressure gas reservoirs 81 are connected by high pressure fittings 83and high pressure tubing 85 to form a single reservoir which isconnected directly to pressure chamber 79 by means of fittings 87 and 89and high pressure tubing 91. Gas reservoirs 81 are charged prior to useby means of an external gas supply which is subsequently disconnectedprior to use of the system so that the system can be operated for aperiod without requirement for outside connection to a gas supply.

Pressure chamber 79 receives gas from the high pressure gas supplythrough fitting 89 which is a threaded fitting of common availabilitycapable of being sealed in such a manner as to prevent any loss of gaseither through the threaded connection into housing 13, or through thejunction with supply tube 91. Since pressure chamber 79 is also incommunication with borehole 73, which is unpressurized, by way of guidehole 77, a high pressure seal must be provided at this location whichboth permits axial motion of core rod 65 while simultaneously preventingleakage of gas through guide hole 77. This is accomplished by means of aradial o-ring 93 which seals valve core rod 65 against plate 95. Plate95 is sealed against housing 13 by means of face o-ring 97. Both o-ringseals, in combination, achieve the necessary seal for pressure chamber79 while permitting axial motion of valve core rod 65.

Pressure chamber 79 is in communication with expansion nozzle 99 throughthroat, or fluid passage 101 of expansion nozzle 99. As was previouslydescribed, and as discussed in further detail hereinbelow with regard toFIG. 6, high pressure valve seat 67 for valve core rod 65 is formed inexpansion nozzle 99 at throat 101. Since one possible method offabricating housing 13 is to bore pressure chamber 79 from one side ofhousing 13, for this embodiment of the invention, expansion nozzle 99may be fabricated separately and subsequently bolted to housing 13 bymeans of fasteners 103. Sealing of expansion nozzle assembly 99 tohousing 13 may be achieved by radial o-ring 105 (as also shown in FIG.5).

FIGS. 2 and 3 illustrate side and top views of the cold gas thrusterembodiment of the invention which show, in addition to those featuresheretofore described, one possible arrangement for mounting onboardmicrocontroller subsystem 107 and energy storage and amplificationsubsystem 109 (preferably including a high slew rate, high amperage,high voltage linear power amplifier) utilized to provide (pursuant to aprogram stored in microcontroller subsystem 107) the calibrated outputvoltage for driving stack 19. These are affixed to opposing sides of gasreservoirs 81 by means of brackets 111 which are connected to housing 13by fasteners 113. It is further illustrated in FIG. 2 and 3 thatboreholes, or cavities, 21 and 73 for piezoelectric stack 19 and forguide rod 63 and plug 71, respectively, are machined in such a manner soas to lie on the plane which passes through the centerline of thethickness of housing 13. Bracket 115, shown in FIG. 3, is provided withthreaded holes which may be used to mount the invention on the structureto be controlled and/or tested.

Microcontroller subsystem 107, with appropriate feedback data, may beused to enhance and refine repeatability. For example, on-board memorycan be used to store data indicative of event characteristics,structural response characteristics (i.e., the responses to loading ofthe structure to be controlled and/or tested, such as force andacceleration feedback) and control signal parameters. The residentprogram of the microcontroller may then be applied to refine controlsignal parameters in view of the data to optimize testing and/orcontrolling of the structure.

Referring now to FIGS. 4 and 5, during operation, a step change inpositive direct current voltage will cause piezoelectric stack 19 toexpand to a degree proportional to the step change in voltage. Sincestack 19 is connected to a rigid internal reaction surface at bearingseat 41, all expansion occurs at the lower end and is transferredthrough bearing 27 to tapered bearing seat 45 which is machined on theshort side of lever 33. The vertical displacement of piezoelectric stack19 therefore causes bearing seat 45 on lever 33 to be moved downward andfor lever 33 to rotate about hinge 35. Consequently, and as will beexplained in detail below, bearing 47 on the long side of lever 33 iscaused to move upward to thus unseat valve core tip 117 from valve seat67 and initiate loading as gas is expanded through nozzle 99.

This inversion of displacement direction is required becausepiezoelectric stack 19 is unable to effectively transmit loads intension and because of the flow requirements through nozzle 99 (i.e.,typically in this embodiment laminar flow of the high pressure fluidflow through nozzle 99 is required). A positive return mechanism must beavailable to close core tip 117 against valve seat 67 for the samereason. This is effectively accomplished by compression spring 69 whichis chosen such that the precompression force satisfies two criteria:first, it must be capable of sealing valve seat 67 such that no gasand/or propellant is permitted to escape through expansion nozzle 99when piezoelectric stack 19 is in the uncharged state; and second, theprecompression force must be capable of accelerating lever 33 and valvecore rod assembly (valve core rod 65, guide rod 63 and coupler 57)downward towards a closed valve position in such a manner as to alwaysexceed the contracting acceleration of piezoelectric stack 19 as thevoltage signal which drives the stack is diminished. This is required inorder to maintain all bearings (27, 29, and 47) in a state of continualcompression to avoid the possibility of separation and subsequent shockloading and noise in the impulse.

FIG. 5 is a detailed illustration of pressure chamber 79. In thepreferred embodiment of the invention, this chamber is milled fromhousing 13 as a circular borehole. Radial o-ring 105 and optional backupring 119 provide a high pressure static seal between nozzle 99 andcircular wall 121 of chamber 79. Fasteners 103 are sized to resist theresultant force acting to expel nozzle 99 from housing 13 due to thehigh internal pressure inside pressure chamber 79. Face o-ring seal 97is precompressed against housing 13 by plate 95 by means of fasteners123 and prevents escape of gas around plate 95 and into guide hole 77.O-ring seal 93 and optional backup rings 125 prevent escape of gasthrough guide hole 127 in plate 95 through which valve core rod 65passes. Seal 93 additionally serves as a viscous damper for valve corerod 65 to thereby minimize elastic rebound when core rod tip 117 closeswith valve seat 67.

Upward motion of valve core rod 65 will permit high pressure gas toexpand through nozzle 99 and thus create thrust 50 (in the directionindicated by the arrow). In furtherance thereof, high pressure gasand/or propellant received through supply inlet 129 to chamber 79 isdelivered through fitting 89 and gas supply tubing 91 which haveinternal diameters significantly larger than the throat diameter (D inFIG. 6) of throat 101 of expansion nozzle 99 in order to maintain fullydeveloped flow at all times when the valve is open.

FIG. 6 is a detailed illustration of the relationships of valve core tip117 if valve core rod 65 and valve seat 67 (in combination, providing avolumetric control valve capable of producing metered gas flow to nozzle99 having suitable laminar flow characteristics for the degree ofcontrol necessary in the contemplated applications of the inventionherein disclosed). Valve core rod mating surface 131 is precision groundto have a slope A, for example of 29.5 degrees, and thus an includedangle of 59 degrees. Core rod tip 117 is precision ground to a flatterangle B, for example of approximately 30 degrees from horizontal (120degrees included angle), so as not to come into contact with valve seat67. Valve seat 67 is machined with a tapered angle C, for example of 30degrees (a 60 degree included angle). Since angle C is slightly largerthan angle A, initial sealing of the valve occurs at expansion nozzlethroat 101.

FIG. 7A, 7B and 7C illustrate in detail rigid lever 33, hinge 35, andsupport 37. During normal operation, expansion of piezoelectric stack 19in response to a controlled step change in the direct current signalwill in turn exert force on tapered circular bearing seat 45 on theshort side of the lever 33 whose fulcrum is approximately defined athinge 35. In turn lever 33 rotates clockwise about hinge 35 causingbearing seat 49 on the long side of lever 33 to be forced upward,thereby generating force as it reacts against precompression spring 69(see FIG. 4). The upward displacement at bearing seat 49 has been shownto be, to within four significant figures, equal to the expansion ofpiezoelectric stack 19 times the ratio of length E divided by length F.

The tapered shape of hinge 35 is necessary in order to minimize both themass of the lever (in order to reduce inertially induced forces andmoments as the piezoelectric stack expands) as well as to minimizeflexural deformations relative to the undeformed top surface of thelever due to the action of applied forces at seats 45 and 49. Hinge 35is designed to be as thin as possible in order to minimize rotationalresistance about an axis perpendicular to the principal plane of theamplifier. The height G of the hinge is selected to be as tall aspossible while avoiding the possibility of buckling under the combinedcompressive loads at seats 45 and/or 49. The hinge width H is selectedto prevent both bearing failure of the hinge as well as to inhibit thelikelihood of lever 33 resonating in a torsional mode. These designcriteria lead to the requirement for the amplifier to be fabricated froma very high strength, low modulus material with a relatively long linearelastic stress-strain curve such as titanium alloy. Preferably,mechanical displacement amplifier 31 is monolithically milled from thesame base block of such material so that an overall integrated unit isprovided (i.e., hinge 35 is integral to both lever 33 and support 37while yet providing negligible resistance to desired rotation).

In order to minimize stress concentration and to alleviate thelikelihood of fatigue cracking, hinge 35 is machined or otherwisefabricated with curved interfacing radii I lever 33 and support 37.Hinge width H (and also the width of lever 33) is less than width J ofsupport 37 such that when support 37 is affixed to housing 13 by meansof fasteners 133 there will be no interference with the housing wall aslever 33 rotates.

FIG. 8 illustrates a second embodiment 135 of the invention for apressure-fed bipropellant thruster of a type that can be used for veryhigh precision attitude control of spacecraft. There are severalfundamental differences between the operation of the invention shown inFIG. 8 and that for the cold gas thruster described in FIGS. 1 through3. The primary difference is that the propellant medium consists of twoliquids which are stored inside non-reactive chambers 137 and 139 (anoxidizer in chamber 137 and a fuel in chamber 139). Chambers 137 and 139are in turn pressurized by means of high pressure inert gas sources 141and 143 which are in turn connected by means of delivery tubes 145 and147 to expansive bladders 149 and 151 which expand and pressurizechambers 137 and 139, respectively, in such a manner as to occupy thevolume of space vacant of oxidizer or fuel and to apply uniform pressureto the remaining oxidizer or fuel.

Acting under the influence of the high internal pressure from pressurevessels 141 and 143, oxidizer and fuel are forced to flow throughdelivery tubes 153 and 155, respectively, which communicate with valvechambers 157 and 159, respectively. Elements 141, 145, 149, 137 and 153comprise oxidizer pressure-fed delivery system 161. Elements 143, 147,151, 139 and 155 comprise fuel pressure-fed delivery system 163.

Functional unit 165 is comprised of all of the basic componentsdescribed for the high speed valve system in FIGS. 1 through 7 less thecold gas supply system and expansion nozzle 99. Unit 165 provides forhighly responsive monitoring and metering of oxidizer from valve corechamber 157 through valve seat 167. Unlike the cold gas thrusterembodiment of the invention, valve seat 167 is in communication withdelivery tube, or passage 169 which is in communication with combustionchamber 171. A supplementary nozzle 173 may be used to direct anddisperse the flow of oxidizer into combustion chamber 171.

Functional unit 175 is likewise comprised of all of the basic componentsheretofore described in FIGS. 1 through 7 less the cold gas supplysystem and expansion nozzle 99. Unit 175 provides for highly responsivemonitoring and metering of fuel from valve core chamber 159 throughvalve seat 177. Again, unlike the cold gas thruster embodiment of theinvention, valve seat 177 is in communication with delivery tube, orpassage 179 is in communication with combustion chamber 171, and asupplementary nozzle 181 may be used to direct and disperse the flow offuel into combustion chamber 171.

A typical oxidizer for use in embodiment 135 of the invention may benitrogen tetroxide whereas a typical fuel may be monomethyl hydrazine,although any oxidizer and fuel combination which is hypergolic in naturemay be utilized. The impingement pattern of nozzles 173 and 181 may beoptimized to produce uniform and complete burning of the constituentswithin combustion chamber 171. The combustion products are then expandedthrough nozzle 183 to produce thrust. It may be appreciated that, due tothe ability to place valve unit 165 and valve unit 175 under separatemicroprocessor control, the mix ratio of fuel to oxidizer, as well asthe flow rates to combustion chamber 171 can be varied at extremelyrapid rates so as to be able to create, on demand, either very small,very rapid control forces or large, rapid control forces (as determinedto be necessary depending, for example, on the nature of the dynamicdisturbing force which must be damped, an attitude control maneuverwhich must be initiated, or a pointing requirement which must bemaintained with a high degree of precision). The reaction control systemembodied in FIG. 8 makes possible extremely rapid control response, aswell as very high precision in both small and large applied forces.

As may be appreciated, this invention provides apparatus and methods foramplitude variable thrust control useful in the precision attitudecontrol and/or pointing and stabilizing of spacecraft and satellites(resulting in less fuel consumption, cycle time between acquisition ofnew targets, and finer pointing stabilization), precision processcontrol as a reagent addition system for semiconductor processing werecorrosive and/or doping gases must be metered precisely to achievedesired deposition or substrate removal thicknesses on the order of amicron, structural research, automotive and/or aerospace fatiguetesting, or even active control of buildings during earth quake or highwind conditions to provide real time damping of lateral forces acting onthe building. Testing has shown the apparatus to provide a minimumcontrollable pulse width of 0.001 second with a lag time between controlsignal to the piezoelectric structure and the onset of thrust of about0.0004 second, amplitude of the force-time pulse being variable over awide spectrum of force levels in a continuous, or linear, manner, asillustrated by the test data in FIGS. 9 through 11.

What is claimed is:
 1. A thruster comprising;first storage means forstoring at least a first fluid under pressure; a thruster nozzle; acontroller for developing and generating a control signal; and firsthigh speed, pulse duration and amplitude variable valving meansoperatively associated with said first storage means, said controllerand said thruster nozzle for metering said first fluid from said firststorage means to selectively produce either of continuously variable andpulsed thrust through said thruster nozzle and being capable of arepeatable pulse duration of less than 0.01 second and a lag timebetween control signal generation and onset of thrust of less than 0.01second.
 2. The thruster of claim 1 wherein said thruster is one of acold gas, monopropellant, and bipropellant reaction control thruster. 3.The thruster of claim 1 wherein said valving means includes a co-firedpiezoelectric stack capable of fully developed strain within about 10microseconds.
 4. The thruster of claim 3 wherein said valving meansincludes a mechanical displacement amplifier engaging said stack foramplifying displacement caused by said strain.
 5. The thruster of claim1 wherein said control signal has a duration and a variable parameter,and wherein said valving means includes c core and a seat movement ofsaid core allowing metering of said first fluid, said movement beingproportional to said variable parameter of said control signal.
 6. Thethruster of claim 1 further comprising second storage means for storinga second fluid, second valving means and a chamber for receiving saidfirst fluid metered through said first valving means and having saidnozzle connected therewith, said second valving means being a highspeed, pulse duration and amplitude variable valving means operativelyassociated with said second storage means and said controller formetering said second fluid from said second storage means to saidchamber.
 7. A high speed, amplitude variable thrust control apparatusfor use with a high pressure fluid supply, said apparatus comprising:athruster unit; valve means configured to retain the fluid under highpressure when in the closed position; control signal input means forselectively providing a control signal having a duration and a variableparameter; structure connected with said control signal input means andcapable of structural response producing a known amount of displacementin a first direction proportional to said variable parameter of saidcontrol signal when said signal is provided from said control signalinput means to said structure; a displacement amplifier operativelyassociated with said structure for amplifying said displacement; andcoupling means for applying said amplified displacement to open saidvalve means and thus meter a volume of the fluid therethroughproportional to said variable parameter of said control signal.
 8. Theapparatus of claim 7 wherein said amplifier is a mechanical displacementamplifier comprising a monolithically milled lever, hinge and support,said amplifier configured to reverse direction of said amplifieddisplacement from said first direction.
 9. The apparatus of claim 7wherein said variable parameter is voltage level, and wherein saidstructure includes a co-fired piezoelectric stack.
 10. The apparatus ofclaim 7 wherein said valve means has a core and a portion integral withsaid thruster unit, said core being displaced an amount proportional tosaid control signal variable parameter to allow fluid movement throughsaid portion.
 11. The apparatus of claim 1 wherein said control signalinput means includes a microcontroller.
 12. The apparatus of claim 7wherein said valve means includes a valve seat integral with a throat ofsaid thruster unit and biasing means for positive return of said valvemeans to said closed position.
 13. A high speed, amplitude variablethrust control apparatus for use with a high pressure fluid supply, saidapparatus comprising:a thruster unit having a fluid passage; valve meansconfigured to retain the fluid under high pressure when in the closedposition and including a valve seat integral with said fluid passage ofsaid thruster unit; control signal input means for providing aselectively variable control signal; structure connected with saidcontrol signal input means and capable of structural response producinga known amount of displacement in a first direction proportional to saidvariable control signal when said variable control signal is providedfrom said control signal input means to said structure; and couplingmeans for opening said valve means responsive to said displacementproduced by said structure to thereby meter a volume of the fluidthrough said valve seat of said valve means proportional to saidvariable control signal.
 14. The apparatus of claim 13 furthercomprising a displacement amplifier operatively associated with saidstructure for amplifying said displacement, said coupling means applyingsaid amplified displacement to open said valve means.
 15. The apparatusof claim 13 wherein said control signal input means develops saidvariable control signal having a signal duration as short as 0.001second.
 16. The apparatus of claim 13 wherein said valve means begins toopen within as little as 0.0005 second of provision of said variablecontrol signal from said control signal input means to said structure.17. The apparatus of claim 13 wherein said control signal input meansdevelops said variable control signal including a selected duration anda selected voltage level.
 18. The apparatus of claim 13 wherein saidcontrol signal input means includes storage and processing means forstoring operational data and utilizing said data to refine said variablecontrol signal and thereby desired thrust response.
 19. The apparatus ofclaim 13 wherein said thruster unit includes a chamber for receipt ofsaid metered volume of said fluid through said valve seat of said valvemeans and for mixing thereat with a second fluid metered independentlyinto said chamber.
 20. The apparatus of claims 13 wherein said fluidpassage of said thruster unit is a throat.